Japanese Patent Application Laid-Open Publication No. 2001-85611 (Patent Document 1) describes a power module in which a plurality of power elements are mounted on a ceramic substrate through a plurality of conductive layers.
Also, Japanese Patent Application Laid-Open Publication No. 2003-332481 (Patent Document 2) and Japanese Patent Application Laid-Open Publication No. 2011-77087 (Patent Document 3) describe a semiconductor module substrate obtained by bonding a copper plate for a wiring circuit onto an upper surface of the ceramic substrate and a copper plate for heat release onto a lower surface of the ceramic substrate.